This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Soluble proteins enter the secretory pathway in the endoplasminc reticulum and then move to the Golgi complex. If they have no specific sorting information on them, they exit the Golgi and are secreted to the cell exterior. Therefore, sorting away from this ?bulk flow? requires both that the soluble protein carries a signal, and that an integral membrane receptor protein recognizes the signal and pulls the soluble protein into a vesicle that will carry it to a different destination. Somehow, within the plant Golgi apparatus, one receptor (BP80) recognizes one type of signal and pulls a soluble protein into the lytic vacuole pathway, while a different receptor (RMR) recognizes a different signal and pulls a different soluble protein into the protein storage vacuole pathway. A similar process occurs in the mammalian Golgi complex, except the lytic pathway receptors are the mannose-6-phosphate receptor and sortilin. In order to understand this complex but decisive sorting mechanism, we have decided to solve the crystal structure of the receptor molecules.